Surface wave transmission



N O I s S I Oct. 13, 1970 Filed April 20, 1967 INVENTOR THEODORE HAFNER ite St es 3,534,303 SURFACE WAVE TRANSMISSION Theodore Hafner, 265 Riverside Drive, New York, NY. 10025 Filed Apr. 20, 1967, Ser. No. 637,321 Int. Cl. H0111 3/12; H0411 5/00 US. Cl. 333-95 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the transmission of electromagnetic Waves and, more specifically, to the transmission of surface waves along one or more conductor elements.

This invention is related to application Ser. No. 83,244, filed Jan. 17, 1961 now abandoned, application Ser. No. 421,539, filed Dec. 28, 1964 now Pat. No. 3,290,626, and application Ser. No. 587,611, filed Oct. 18, 1966.

It has been found that symmetrical transmission lines, and especially two-wire transmission lines, after extension over considerable distance, experience a degradation of their field characteristic causing increasing loss and standing waves, making long distance transmission of an extended frequency range unreliable, if not unfeasible, unless complex and expensive measures are provided to assure field symmetry and wave propagation at acceptable loss.

Experiments underlying this invention have shown that the degradation of the symmetrical wave field at such an extended distance, say a few thousand feet or a mile, is due to the fact that the symmetrical wave of the twowire line, consisting of the two phase opposed waves of the individual wires, tends to become two more or less phase equalized waves of surface wave character, depending of course on the other means and conditions, such as nature of dielectric and suspension, required for the propagation of surface waves proper.

One of the objects of the invention is an asymmetrical, twin-conductor line, adapted to operate in an arrangement close to the wall, such as the top, sides or bottom of a railway or subway tunnel to permit train to station I and/or station to train communication, signaling and controlling, with a relatively large band width such as 50 mc. and more in a relatively low frequency range such as VHF, UHF and above and due to the surface wave characteristic of the propagated waves, with least interference with any radiated channels existing in the neighborhood.

A more specific object of the invention is an asymmetrical two-conductor transmission line consisting of wire conductors extending along the wall of a tunnel or similar structure, at a distance therefrom which is large against the conductor dimensions, but smaller than wave length, and which is attached to the wall facing these conductors; and extending substantially parallel thereto, a conducting sheet of a width which is also larger than the conductor dimensions, but smaller than wave length, preferably somewhat larger than the distance of the wire conductors from the sheet.

As another object of the invention, the conducting sheet is in the form of a trough or U-shaped channel with side walls extending up to the height of the wire conductors.

3,534,393 Patented Oct. 13, 1970 As a termination of the asymmetrical two conductor lines, the sheeted conductor at its end portion is surrounded by a second sheeted conductor which is provided with a cut-out to permit matching of the line with a coaxial cable connected to the two conductors and arranged in the space between said conducting sheet.

These and other objects of the invention will be more fully apparent from the drawings annexed herewith, in which:

FIGS. 1 and 2, in front and side elevation, respectively, show an asymmetrical twin-conductor line as may be used to produce a field with minimum loss inside a railroad tunnel when attached to the top wall of the tunnel.

FIG. 3 shows in perspective an exploded view of the assembly of FIGS. 1 and 2.

FIG. 4 shows part of the line suspension at an enlarged scale.

FIG. 5 shows an example of terminals of an asymmetrical twin conductor line, and

FIG. 6 shows an enlarged portion of such termination.

FIG. 7 illustrates an asymmetrical twin conductor line as installed on or near the ground of a subway tunnel.

FIGS. 1 and 2 illustrate an asymmetrical twin conductor line consisting of a conducting wire 1 which may consist of copper plated steel provided with a dielectric coating to produce a surface wave field of such shape and dimensions as to have a minimum loss due to wall proximity and a maximum reach into the tunnel itself to permit effective train to station communication over as many tracks as possible and over as long a distance along tracks as possible, and a relatively fiat or sheeted conductor 2 attached to the top wall 3 of a tunnel and extending across the wall for a distance substantially larger than the cross-sectional dimensions of wire conductor 1.

Conductor 1 is attached to wall 3, or sheet 2, by insulating straps or hangers 4, 5 shown in FIG. 4, at a predetermined distance which is larger than the crosssectional dimensions of conductor 1, but not larger and preferably smaller than the width of conductor sheet 2 to assure the desired minimum loss and wave shaping effects.

As apparent from FIGS. 1 and 2 and more clearly from the exploded view of FIG. 3, sheet 2 is a trough or U-channel shaped. It should be noted that the smaller the height and the larger the width of the channel the less will the resulting surface wave field be affected by the wall.

If conducting sheet 2 is trough or U-channel shaped, conductor 1 preferably in the form of a polyethylene coated copper plated steel wire is arranged at a distance from the bottom of sheet 2 corresponding to the height of the trough or the U-shape.

Field extension and radiation can also be controlled by adjusting the sag of wire 1 as apparent from FIG. 2 at 13. Since increased sag also increases wall losses, optimum data can be determined experimentally.

As a further advantage of invention no special launcher will be required for this surface wave trans mission line.

As shown in FIG. 5 termination is provided by plac ing upon the end of the channel 2 schematically indicated at 13 a smilar channel 14 provided with a triangular cutout schematically indicated at 15 as shown in FIG. 6 at an enlarged scale. Top channel 2 and bottom 14 assembled as shown in FIG. 5 constitute a termination of the line whereby wire or surface wave conductor 1 can be simply connected to the inner conductor of a coaxial cable 16 which in turn may be connected to any terminal equipment as required.

In the assembly shown in FIG. 5 the slanted walls of the upper channel 13', are bent to right angles.

The trough or U-channel 2 itself can be made of thin aluminum sheet which could be bent to the desired shape during construction of the line.

It is attached to wall 3 through holes 6, 7 by means of steel straps 8 of quarter wave length dimension, and screws 9, 10 drilled or pushed into the concrete of wall 3; straps 8 support the hangers 4, which, as shown in FIG. 4, may be of fiberglass for maximum strength and minimum loss, and which hold the conductor 1 by means of nylon rivets 11, 12.

The entire assembly is attached to the ceiling of tunnel 3 as shown in FIG. 2, in such a way that straps 8 provide support for wire 1, hangers 4, 5 and also serve to fasten channel 2 against the ceiling.

Hangers 4, 5 themselves, as apparent from FIG. 4, can be mounted around wire 1 by simply prying them open. The lower one 11 of the rivets 11, 12 provide the gripping of the wire 1, while the upper rivet 12 prevents the hangers 4, 5 from coming off steel strap 8.

The double hanger support as shown in FIGS. 1, 2 and 3 reduces wave reflections caused by the individual supports themselves.

In another embodiment of the invention, which is especially applicable to railroad and subway communication, and which is schematically indicated in FIG. 7, the two conductor transmission line is attached between rails 17 and 18 to the bottom of the track. In this case the inside of the conductor channel 19 is placed with its open end upside. For example, for a frequency range of around 150 mc./s., it may have a width of around 4 inches and a height of 6-8 inches; it is at least partially filled with foam plastic, for example polystyrene or polyurethane as indicated at 20. The wire or cable conductor is at least partially embedded in the foam as schematically indicated at 21.

In order to protect the inside of channel 19 from dirt it is provided with a dielectric cover schematically indicated at 22 and consisting for example of fiber glass or polyethylene sheeting.

In this way the transmission line may also be attached by channel 19' on the ground in the manner shown in FIGS. 1 and 2 with respect to a wall, or it may be otherwise arranged on the ground, with a train being able to pick up the field passing through dielectric cover plate 22.

While the invention has been described and illustrated with respect to the specific embodiment-s submitted herein, it is not limited thereto, but it may be used, applied, modified, attached and mounted in any appropriate manner, without departing from the scope of this disclosure.

What I claim is:

1. In a surface wave transmission system for support on a wall or like substantially continuous structure, a first substantially linear conductor extending spaced parallel to the wall and coated with a dielectric to maintain a surface wave of finite diameter in at least part of the space around it, and a second conductor in the form of a trough arranged on the wall, and facing said linear conductor parallel thereto, said sheet having side walls extending to the height of the linear conductors; having a width which is large against the crosssectional dimensions of the linear conductor; the two conductors being insulatingly spaced from each other at a distance not larger than the width of said sheet; the linear conductor being supported by means of at least one pair of hangers arranged at a quarter wavelength distance.

2. In a surface wave transmission system for support on a wall or like substantially continuous structure, a first substantially linear conductor extending spaced parallel to the wall and coated with a dielectric to maintain a surface wave of finite diameter in at least part of the space around it, and a second conductor in the form of trough arranged on the Wall, and facing said linear conductor parallel thereto, said sheet having side walls extending to the height of the linear conductor; having a width which is large against the cross-sectional dimensions of the linear conductor; the two conductors beng spaced from each other at a distance not larger than the width of said sheet; the two conductors being insulatingly supported one on the other; said trough at its termination being covered with a second trough, and said second trough being provided with a triangular cutout to provide matching; there being arranged a coaxial cable along the axis of the linear conductor, the inner conductor of which extends into said linear conductor.

3. In a surface wave transmission system for support on a wall or like substantially continuous structure, a first substantially linear conductor extending spaced parallel to the wall and coated with a dielectric to maintain a surface wave of finite diameter in a least part of the space around it, and a second conductor in the form of a trough arranged on the wall, and facing said linear conductor parallel thereto, said sheet having side walls extending to the height of the linear conductor; and having a width which is large against the crosssectional dimensions of the linear conductor; the two conductors being insulatingly spaced from each other at a distance not larger than the width of said sheet; the trough being at least partially filled with foam, and the linear conductor being at least partially embedded in said foam; the top of said channel being covered by a dielectric sheet.

4. In a surface wave transmission system for vehicular communications along a predetermined path, a first substantially linear conductor extending spaced parallel to said path and coated with a dielectric to maintain a surface wave of finite diameter in at least part of the space around it, means for launching a substantially pure surface wave and a second conductor in the form of a sheet arranged along said path, facing said linear conductor parallel thereto, and having a width which is large against the cross-sectional dimensions of the linear conductor; the two conductor-s being insulatingly spaced from each other at a distance not larger than the Width of the conducting sheet leaving sufiicient space on both sides of said linear conductor so as to permit at least a portion of the surface wave which is terminated at one side by said sheet, to extend on the other side into said path so as to be picked up by a vehicle passing along said path.

5. System according to claim 4, wherein said conducting sheet is of U-channel shape, with the side walls slanted to the outside, forming an angle of more than with the bottom of the sheet.

6. System according to claim 4 wherein said conducting sheet is of U-channel shape, and wherein for attachment to the ceiling of a tunnel, the height of the U-channel is substantially smaller than its width.

7. System according to claim 4, wherein said conducting sheet is of U-channel shape, and wherein for attachment to the bottom of a tunnel, the height of the channel is larger than the Width.

References Cited UNITED STATES PATENTS 2,478,133 8/1949 Shanklin. 2,721,312 10/1958 Grieg et al.

OTHER REFERENCES Harvey, A. F., Microwave Engineering, 1963, Academic Press, New York (page 412 relied on).

PAUL L. GENSLER, Primary Examiner U.S. Cl. XR. l792.5, 82 

